The present invention relates to safety relief valves for use with gases or liquids on a pressurized system, such as pressure vessel or a flow line.
Safety relief valves are commonly used on pressure vessels or pipelines to relieve temporary pressure surges in excess of the safe pressure the vessel or pipeline can withstand. Safety relief valves have the advantage of responding very quickly to pressure changes in pressurized systems to which they are attached. Safety relief valves move to a fully open position almost immediately after the pressure within the system rises above a user-determined set pressure. This allows excess fluid pressure to escape quickly. Then, when sufficient pressure has escaped, safety relief valves quickly move back to a closed position. For an example of a safety relief valve, see U.S. Pat. No. 4,932,434, which is herein incorporated by reference in its entirety.
Existing safety relief valves do, however, have some problems. One problem is that fluid flowing through a safety relief valve must change direction inside the valve body due to the valve body outlet being located at a ninety degree angle in relation to the valve inlet. The redirection of flow causes internal moveable parts to shift towards the valve body outlet during valve cycling, resulting in interference between the moveable parts and related stationary guide members. Part shifting causes the guide surfaces of parts to rub together resulting in damage, such as galling, to occur on the guide surfaces. Galling can be defined as a condition where excessive friction between sections on two mating parts results in localized welding with subsequent splitting and a further roughening of the rubbing surfaces of one or both of the two mating parts. Part shifting also causes problems when the valve closes. As the moveable parts attempt to realign with the inlet upon valve closure, undesirable impact occurs between the face of the moveable parts and the inlet resulting in impact damage to the parts.
See, for example, the safety relief valves described in U.S. Pat. No. 4,799,506 (hereinafter the '506 patent), which is herein incorporated by reference in its entirety, and U.S. Pat. No. 8,413,955 (hereinafter the '955 patent), which is herein incorporated by reference in its entirety. In these designs, a disk member rests upon a valve seat on an inlet with a stem member attached to the disk member. The stem member provides guidance to the disk member, and a guide member with an internal longitudinal guide bore acts to provide guidance to the stem member. This type of disk member guidance arrangement is preferable, since the guide surfaces are located away from the general path of flow, which lessens the possible build-up of foreign particles between the guiding members. When the disk member is removed from the valve seat, fluid escapes and exits the valve body through the outlet, which is located at a ninety degree angle in relation to the inlet. The redirection of fluid from the inlet towards the outlet shifts the disk member and stem member towards the valve body outlet. The shifting of the disk member towards the outlet creates detrimental contact between the stem member and the guide bore during valve cycling. Disk member shifting towards the outlet, coupled with repeated cycling of the disk member, causes damage to the stem member and the guide bore. In a worst case scenario, the stem member material may yield or fail. Damage to the members is exacerbated during high pressure venting cycles, due to the increase in contact force between the stem member and the guide bore created by high-powered flow forces exiting the valve body outlet. In the '506 and '955 patents, the stem member serves as the main means of guidance for the disk member when the disk member is removed from the valve seat, and close fit tolerances are necessary between the stem member and the guide bore for repeatable valve performance. Any damage on the stem member or guide bore can interfere with the cycling of the disk member, thereby changing valve opening and closing characteristics, which makes valve performance less predictable.
The shifting of the disk member towards the outlet also creates a problem when the valve closes. As the disk member attempts to realign with the inlet upon valve closure, undesirable contact occurs between the spherical sealing surface of the disk member and the top surface of the valve seat. The repeated realignment of the disk member with the valve seat during valve closing results in damage on the disk member due to repeated impact. This is especially undesirable, since the spherical face of the disk member is used in combination with the valve seat to provide a valve seal at the inlet. Disk member damage at the spherical sealing surface will result in the valve continuously leaking pressurized fluid from the inlet.
Another problem with existing safety relief valves is that they tend to utilize a sliding-fit disk member and skirt member design with the skirt member providing disk member guidance. See, for example, the safety relief valves described in U.S. Pat. No. 2,597,057 (hereinafter the '057 patent), which is herein incorporated by reference in its entirety, and U.S. Pat. No. 5,341,838 (hereinafter the '838 patent), which is herein incorporated by reference in its entirety. In the '057 and '838 patents, when the disk member is raised from an inlet so that fluid escapes, a portion of the skirt member obstructs the flow path as fluid flows around a blow-down control mechanism on the inlet, so that the fluid accumulates above the disk member in a closed bonnet. As fluid moves around the disk member and into the bonnet, foreign fluid particles accumulate between the sliding surfaces of the disk member and the skirt member. The closely fitted outer diameter of the disk member and inner diameter of the skirt member serve to guide the disk member and control the time it takes for fluid from the inlet to enter and exit the closed bonnet. This condition is used to control the blow-down value of the valve, but in doing so, the sliding-fit parts are coated with contaminates from the fluid. The build-up of foreign particles from contaminated fluids causes interference with disk member movement. This interference can affect the amount of inlet pressure needed to operate the valve, thereby changing valve opening and closing characteristics, which makes valve performance less reliable.
In addition to the above-mentioned problems, safety relief valves can vary in quality in a number of ways. Different safety relief valves vary in their ability to attain high coefficients of flow, their performance reliability, their durability, their cost to manufacture, and their ease of use.